Modified rubber powders comprising silicatic fillers prepared from precipitation suspensions, process for their preparation and their use

A process for preparing silica-filled rubber powder, comprising:

• contacting:
• a water-soluble salt containing aqueous silica-precipitation suspension, with
• at least one member selected from the group consisting of rubber latex, rubber solution, and rubber emulsion,
• to form a mixture;
• and
• precipitating to produce a silica-filled rubber powder
• wherein the process further comprises:
• (a) mixing one or more organosilicon compound(s) which contain at least one alkoxy group with the silica-precipitation suspension at a temperature of 10 to 60° C., said organosilicon compound(s) being undiluted, emulsified, or dissolved in water, and optionally in the presence of one or more surface-active substances, to form a masterbatch, and dividing the masterbatch into first and second batches;
• (b) mixing the first batch with the rubber latex, rubber solution, or rubber emulsion and adding at least one first acid to lower the pH to between 8.0 and 6.5 inclusive to form a mixture and precipitating silica-filled rubber particles;
• (c) adding the second batch to the mixture and adding at least one second acid to lower the pH to between 6.5 and 2.6 inclusive to form a mixture and precipitating silica-filled rubber particles;
• (d) isolating the precipitated silica-filled rubber particles;
• (e) optionally, washing the precipitated silica-filled rubber particles to obtain salt-free and pH-neutral precipitated silica-filled rubber particles;
• and
• (f) drying to obtain the silica-filled rubber powder.